Tissue harvesting device and method

ABSTRACT

A tissue harvesting method and device for obtaining micrograft tissue particles within the size range of 50-1500 microns, and more preferably 500-1000 microns, and most preferably 600 microns. The particles may be processed after a piece of donor tissue has been excised from the donor site, or processed into the desired size directly at the donor site, and thereafter excised. Cutters having blades or cutting edges spaced in the range of 50-1500 microns are utilized to obtain particles within the desired size range. An elastomer is positioned between the cutting edges to push the excised particles out of the blades for ease of use.

CROSS-REFERENCE TO RELATED APPLICATION

This is a division of co-pending application Ser. No. 10/442,488entitled “Tissue Harvesting Device and Method,” filed May 21, 2003,which is a continuation-in-part of co-pending application Ser. No.10/379,342 entitled, “Tissue Processing System,” filed Feb. 3, 2003; theprior applications are herewith incorporated by reference in theirentirety.

FIELD OF THE INVENTION

The invention relates to a device and method for harvesting dermaltissue. More particularly, this invention relates to a device and methodfor extracting small particles of dermal tissue for transplantation to arecipient site.

BACKGROUND OF THE INVENTION

Traditional skin grafting is accomplished by taking a thin slice ofdermal tissue from a donor site in order to cover a wound site, such asa burn area. In some instances, the slice of dermal tissue is meshed toexpand its size, creating a meshed graft. Traditional devices used toharvest the tissue from the donor site include dermatomes for removing athin slice of the upper layers of skin from a donor site. The slice isthen meshed using traditional techniques to create and expand the sheetof skin tissue that gives the slice a weave-like appearance. The purposeof expanding the skin from the donor site is to increase the amount ofarea on a recipient site that can be covered by the donor site. Some ofthe most desirable expansion ratios currently available are 6:1. Thatis, under the most ideal conditions, skin taken from a donor site wouldbe able to cover a recipient site that is six times larger than thedonor site.

Traditional meshed grafting techniques have been shown to yield 90%viability at the donor site. A slightly lower viability rate occurs fornon-meshed sheet grafts, mostly due to fluid accumulation under thesheet graft. Factors that lead to graft failure include poorcirculation, unclean wounds, patient interference with the graftdressing, obesity, and smoking. Additionally, in at least approximately10% of cases, infection at the donor site occurs. Although such donorsite infections are not likely related to graft failure at the woundsite, they still pose problems for both the patient and caregiver.

As mentioned, traditional meshing techniques yield a most favorableexpansion ratio of 6:1. For example, a 1 cm² donor site can cover a 6cm² wound site. While greater ratios of 9:1 and 12:1 may be possibleusing meshing techniques, there is also a significant delay inepithelialization with such ratios.

Micro grafting techniques, in which the donor tissue is actually mincedin order to achieve a greater than 10:1 expansion ratio, are known inthe art. Such techniques allow for a much greater coverage area from asmall donor site. However, traditional techniques are cumbersome, andoften the viability of the cells is compromised to such an extent thatsometimes less than 50% of the cells are viable when applied to thewound site. Additionally, traditional techniques have thus far beeninadequate in producing viable cells in the range of 500-1500 microns.

Traditional micrograft techniques, dating back to 1963, utilized mincedskin that is between ⅛^(th) inch (approximately 3 mm, or 3000 microns)or 1/16^(th) inch (approximately 1.5 mm, or 1500 microns) in size.However, disadvantages of using pieces larger than 1500 microns havebeen noted. Among the disadvantages are that many of the cells aretrapped within the pieces of skin, and are thus unable to proliferate orproduce new cells required to form new skin. Furthermore, if such largepieces of skin are to be transplanted, the epidermis side of each piecehas to be oriented upwards, and the dermis side oriented downwards. Thismakes the procedure tedious and impractical. Also, the appearance of thenew skin that is produced using particles of this size is poor, oftenhaving a cobblestone appearance.

Other micrografting techniques have utilized minced skin that is 200 to500 microns in size. While sometimes producing cosmetically bettergrafts over the larger micrografts, many of the cells contained in theparticles are rendered non-viable by the process of producing cells ofsuch a small size.

It is therefore an object of this invention to provide a system forobtaining and processing tissue samples from a donor site on the orderof 50-1500 microns in size, such that the vast majority of tissueprocessed at this size is viable when transplanted to a recipient site.It is a further object of the present invention to strike the idealbalance between cell viability and cell proliferation between the sizerange of 500-1500 microns, and most preferably 600 microns, which hasheretofore not been achieved.

Additional objects of the present invention include a significantreduction in the size of the donor site as compared to traditionalmesh-graft procedures; minimizing scarring of the graft site as comparedto traditional mesh-graft procedures; improvement of the pliability oftissue in the graft site; improvement of the cosmetic appearance of thegraft site as compared to current methods; and improvement of graft“take.”

SUMMARY OF THE INVENTION

In accordance with the foregoing objects, the present inventiongenerally comprises a device for harvesting tissue from a donor siteinto particles in the size range of 50-1500 microns, and most preferablyabout 600 microns, such that the particles may produce an expansionratio, or cell proliferation, of at least 6:1 and up to or over 20:1.

The present invention includes a method for cutting and removing tissuefrom a donor site. The typical donor site may be equivalent to asplit—thickness—skin graft (“STSG”). A traditional dermatome may beutilized to obtain the donor sample, or STSG, which is then processedinto smaller micrografts between 50-1500 microns in size. Morepreferably, the micrografts are processed into sizes between 500 micronsand 1500 microns, and most preferably to about 600 microns, which hasbeen shown to yield the greatest viability and proliferation. A cutteris utilized to process the tissue into the desired size. Alternatively,the donor tissue may be processed into the desired size directly on thedonor site, and thereafter removed from the donor site.

The present invention also includes a cutter for processing the tissueinto the desired size range. Several alternative cutters may be utilizedin accordance with the present invention, including roller cutters. Inone embodiment, a roller have having a square-shaped grid pattern ofraised edges is used to achieve tissue particles of the desired size.Alternatively, dual rollers may be utilized, in which each roller has aseries of evenly spaced parallel raised cutting edges, which areoriented perpendicular to the raised edges on the opposing roller. Thedonor tissue or STSG may be passed between the rollers, or the rollersmay be pressed against a single surface of the donor tissue.

Other alternative cutters include die-cast rigid sheets, which may beflat or concave. The rigid sheet is pressed to the donor tissue manuallyor by means of a reciprocating roller. The cutting edges of the rigidsheet include a raised, square-shaped grid pattern, or alternatively, aseries of opposing facing, raised concave cutting edges.

Cutters that may be utilized to process the donor tissue directly at thedonor site include bundled capillary tubes, having a sharpened edge.Other cutters for processing donor tissue that has already been excisedfrom the donor site include a cylindrical press cutter.

Removing the tissue from the cutters, after it has been processed intothe desired size, is accomplished by positioning an elastomer, such asrubber or other flexible material, between the cutting surfaces of thecutters. As the cutter is pushed into the donor tissue, the elastomerretreats from the cutting edge to allow the tissue to be cut. Aspressure is relieved from the cutter, the elastomer returns to itsoriginal position, thereby pushing the cut tissue out from the cuttingedges.

The foregoing has outlined some of the more pertinent objects of thepresent invention. These objects should be construed to be merelyillustrative of some of the more prominent features and applications ofthe invention. Many other beneficial results can be attained by applyingthe disclosed invention in a different manner or by modifying theinvention as will be described. Accordingly, other objects and a fullerunderstanding of the invention may be had by referring to the followingDetailed Description of the Invention, which includes the preferredembodiment

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features and advantages of the invention will now bedescribed with reference to the drawings of certain preferredembodiments, which are intended to illustrate and not to limit theinvention, and wherein like reference numbers refer to like components,and in which:

FIG. 1 is a perspective view of a donor tissue excised from a donor siteusing traditional methods;

FIG. 2 is a perspective view of a cylindrical roller cutter of thepresent invention;

FIG. 3 is a perspective view of donor tissue processed into the desiredsize directly at the donor site in accordance with the presentinvention;

FIGS. 4A, 4B, and 4C are perspective views of a rigid sheet cutter ofthe present invention;

FIG. 5 is a perspective view of a circular blade cutter of the presentinvention;

FIGS. 6A and 6B are perspective views of dual roller cutters of thepresent invention;

FIG. 7 is a perspective view of a stacked microtome cutter of thepresent invention;

FIG. 8 is a perspective view of a bundled capillary tubes cutter of thepresent invention;

FIG. 9 is a cross-sectional view of a cylindrical press cutter of thepresent invention;

FIG. 10 is a perspective view of a stacked disc cutter of the presentinvention; and

FIG. 11 is cross-sectional view of a tissue extraction means of thepresent invention.

DESCRIPTION OF THE INVENTION

Although those of ordinary skill in the art will readily recognize manyalternative embodiments, especially in light of the illustrationsprovided herein, this detailed description is exemplary of the preferredembodiment of the present invention as well as alternate embodiments,the scope of which is limited only by the claims that may be drawnhereto.

Referring now to the drawings, the details of preferred embodiments ofthe present invention are graphically and schematically illustrated.Like elements in the drawings are represented by like numbers, and anysimilar elements are represented by like numbers with a different lowercase letter suffix.

As illustrated in FIG. 1, a donor tissue sample 10, such as asplit-thickness-skin graft (“STSG”) may be removed from a healthy regionof skin tissue 12 using traditional techniques, such as by running adermatome 14 across the surface of the donor site 12. The donor tissue10 is positioned on a flat surface 18, so that the cutter 16 of thepresent invention may be applied to it, as is shown in FIG. 2, in orderto process the tissue into the desired size. In the preferredembodiment, the donor tissue 10 is processed into the desired size rangeof between 50-1500 microns², more preferably between 500-1000 microns²,and most preferably 600 microns². Alternatively, the donor tissue 10 maybe processed into the desired size or size range directly at the woundsite 12, as depicted in FIG. 3. A dermatome 14, or similar traditionaldevice, may be used to excise the processed tissue particles 10 from thedonor site 12.

After the donor tissue is removed from the donor site, the tissue isprocessed by the tissue processor 16, as illustrated in FIGS. 2A and 2B.In an alternative embodiment, the tissue processor 16 cuts the donortissue at the donor site 10 directly. The tissue processor is comprisedof a series of sharpened blades 18 arranged in parallel to one anotherand fixed along an axis 20. The distance 22 between the blades 18 may beadjusted according to the desired size of the tissue sample to beobtained. The preferred distance 22 between each blade 18 is in therange of about 250 microns to 1000 microns. The most preferable distance22 is one of about 16 of the present invention for processing donortissue 10 into particles 20 of the desired size. The cutter 16 consistsof a cylindrical roller 22 in which the cutting surface 24 consists of asquare-shaped grid pattern of raised edges 26, that form blades forcutting the donor tissue 10 into particles 20 of the desired size. Theroller 22 is pressed onto the donor tissue 10 manually, such as byhandles 30 attached along the longitudinal axis 28 of the roller 22, orby an electromechanical actuator (not shown), such as an electric motorand axle along the longitudinal axis 28, similar to that used intraditional dermatomes known in the art.

An alternative embodiment of the cutter 16, as illustrated in FIGS. 4A,4B, and 4C, includes a rigid sheet 34 having a plurality of raisedcutting edges 32. The rigid sheet 34 may be a die as shown in FIGS. 4Aand 4B, in which the cutting edges 32 form a square-shaped grid pattern,in which each grid is the size of the desired particle to be cut fromthe donor tissue 10. Alternatively, the cutting edges 32 may consist ofa series of oppositely facing, raised concave cutters 36, as shown inFIG. 4C. The rigid sheet 34 may be flat, as shown in FIG. 4A, or concaveto aid in manual pressing of the cutter 16 to the donor tissue 10, asshown in FIG. 4B. In such an embodiment, the cutting edges arepositioned on the outer curve 38 of the rigid sheet 34.

The particles may be extracted from the donor tissue after applicationof the rigid sheet 34 cutter 16 by oscillating the sheet 34, such as bya piezo-electric driver, along a vertical axis 40, as illustrated inFIG. 4C. Alternatively, the rigid sheet 34 may be pressed onto the donortissue 10 manually. Other alternative pressing means include use of anarbor (not shown), such as an axle press known in the art, or by meansof a roller actuator 42, that presses the sheet 34 against the donortissue 10 as the roller 44 of the actuator 42 is passed across thesurface of the rigid sheet 34, as shown in FIG. 4A.

Turning now to FIG. 5, there is illustrated a further embodiment of thecutter 16. The cutter is comprised of a series of sharpened circularblades 50 arranged in parallel to one another and fixed along an axis52. A handle 60 may be positioned along an opposing axis 62. Thedistance 54 between the blades 50 may be adjusted according to thedesired size of the tissue sample to be obtained. The preferred distance54 between each blade 50 is in the range of about 50 microns to 1500microns. The more preferable distance 54 is between about 500 micronsand 1000 microns, and most preferably 600 microns. In the preferredembodiment, the space 54 between blades 50 may be adjusted to within thepreferred distances mentioned, or alternatively, fixed to a distancewithin the preferred distances mentioned. The distance 54 between theblades 50 allows for uniform tissue particles to be produced at theideal range of 50 square microns to 1500 square microns. As mentioned,tissue particles within the desired range have been shown to yield thehighest expansion ratio while retaining the greatest viability.

FIGS. 6A and 6B illustrate a further embodiment of the cutter 16, whichconsists of a pair of cylindrical rollers 70 a, 70 b. The firstcylindrical roller 70 a has a first set of raised, parallel cuttingedges 72. The second cylindrical roller 70 b has a second set of raised,parallel cutting edges 74 that are oriented approximately perpendicularto the first set of raised cutting edges 72. The cutting edges 72, 74are separated by between about 50-1500 microns, and most preferably 600microns. In the embodiment depicted in FIG. 6A, the donor tissue 10 ispassed between the first and second rollers 70 a, 70 b, which arerotating in opposite directions around their respective axes of rotation76 a, 76 b. Alternatively, and as depicted in FIG. 6B, the rollers 70 a,70 b rotate in the same direction as they are pressed along the surface80 of the donor tissue 10.

Still another embodiment, as illustrated in FIG. 7, of the cutter 16 ofthe present invention consists of multiple microtomes 82 stacked andseparated by a space 84 within the range of about 50-1500 microns, andmost preferably 600 microns. The microtomes 82 are pressed against thedonor tissue to achieve particles of the size desired.

A further embodiment, shown in FIG. 8, of the cutter 16 of the presentinvention, consists of a bundle 84 of capillary tubes 86 havingsharpened edges 88. The edges 88 are pressed into the donor tissue toextract particles of a size equivalent to the inner diameter 90 of thecapillary tube 86, which is in the range of about 50-1500 microns, andmost preferably 600 microns. An elastomer (not shown), such as softrubber, may be positioned within each capillary tube 86 to aid inextraction of the particles after they have been cut from the donortissue 10. As the capillary tube 86 is pushed into the tissue, theelastomer retreats from the edges 88 of the tube 86, allowing the tissueto be cut. As pressure is relieved, the elastomer returns to itsoriginal position within the tube, pushing the cut tissue particles outof the tubes 86.

A cylindrical press 100, as shown in FIG. 9, may be utilized to cuttissue into a desired size within the range of 50-1500 microns, orpreferably 600 microns, after the donor tissue 10 has been removed fromthe donor site 12. The press 100 is housed within a housing 102 havingan open proximal end 104 and a closed distal end 106, which is closed bythe press 100 itself. An elastomer 108, such as rubber, is fixed to thepress within the housing, and a removable cap 110 is positioned alongthe open proximal end 104 for catching the tissue particles after theyhave been cut. Multiple blades 112 are fixed within the housing 102between the elastomer 108 of the press 100, and the open proximal end104. The donor tissue 10 is placed within the housing 102 between thepress 100, which is removable, and the blades 104. As the press 100passes through the housing 102, the elastomer 108 contacts the tissue 10and forces it into and through the blades 112. The particles, havingbeen cut to the desired size, are trapped within the cap 104.

Still a further embodiment of the cutter 16 is illustrated in FIG. 10.The cutter may consist of multiple serrated discs 120. Slots 122 areformed within the discs 120, which are positioned along an axis 124. Thediscs 120 are fixed along the axis 124 such that a space of between50-1500 microns, or preferably 600 microns, exists between each disc120. A ring 126 of longitudinal blades 128 envelops the discs 120, andconfigured to pass between the serrations of the discs 120. Previouslyexcised donor tissue 10 is placed between the discs 120, cutting theminto the desired particle size as the ring 126 is passed over the discs120.

Extraction of the particles from the blades or edges 130 of the cutter16 is illustrated in FIG. 11. An elastomer 132 is positioned within thespace 134 between the blades or edges 130. As pressure is exerted by thecutter 16 against the donor tissue 10, the elastomer 132 retracts. Thecut tissue trapped in the space 134 between the blades 130 is forced outfrom the space 134 as pressure is relieved from the cutter 16 and theelastomer 132 returns to its original position.

The present invention includes a method of processing harvested donortissue into micrograft particles within the size range of 50-1500microns, and most preferably 600 microns. A further embodiment includesprocessing donor tissue to micrograft particles between 50-1500 microns,and most preferably 600 microns, directly at the donor site, andthereafter excising the particles from their contact points at the donorsite using traditional means, such as a dermatome.

While the above description contains many specifics, these should not beconstrued as limitations on the scope of the invention, but rather asexemplifications of one or another preferred embodiment thereof. Manyother variations are possible, which would be obvious to one skilled inthe art. Accordingly, the scope of the invention should be determined bythe scope of the appended claims and their equivalents, and not just bythe embodiments.

Other features which are considered as characteristic for the inventionare set forth in the appended claims.

Although the invention is illustrated and described herein as embodiedin a Tissue Harvesting Device and Method, it is nevertheless notintended to be limited to the details shown, since various modificationsand structural changes may be made therein without departing from thespirit of the invention and within the scope and range of equivalents ofthe claims.

The construction and method of operation of the invention, however,together with additional objects and advantages thereof will be bestunderstood from the following description of specific embodiments whenread in connection with the accompanying drawings.

1. A cutter for processing tissue into particles suitable fortransplantation, comprising: (i) a first cylindrical roller, having afirst set of raised, parallel cutting edges; and (ii) a second rollerhaving a second set of raised, parallel cutting edges; and (iii) whereinthe first cylindrical roller is disposed proximal to the second rollersuch that a donor tissue can be passed between the first cylindricalroller and the second roller and wherein said first set of raisedcutting edges is approximately perpendicular to said second set ofraised cutting edges.
 2. The cutter of claim 1 wherein said cuttingedges of said first set of raised, parallel cutting edges are separatedby between about 50 microns and 1500 microns.
 3. The cutter of claim 1wherein said cutting edges of said first set of raised, parallel cuttingedges are separated by about 600 microns.